Carbon Dioxide in Blood

Question 1

Which is more soluble: oxygen or carbon dioxide?

Answer 1

Carbon dioxide

Question 2

How much more carbon dioxide is in arterial blood compared with oxygen?

Answer 2

Arterial blood has almost 2.5x as much CO2 than O2

Question 3

What is the most important role of Co2 in the blood?

Answer 3

Control of pH

Question 4

What is the range that arterial blood pH must be kept within?

Answer 4

pH 7.35-7.45

Question 5

How do you work out the concentration of dissolved CO2?

Answer 5

Solubility x pCO2

solubility factor for CO2 is 0.23

Question 6

What does dissolved CO2 react with water to form?

Answer 6

Carbonic acid

Question 7

What does carbonic acid very quickly dissociate to?

Answer 7

H+ and HCO3-

Question 8

What does the direction of the reaction between carbon dioxide and water depend on?

Answer 8

Dependent on concentrations of CO2 and bicarbonate - moves from higher concentration to lower concentration

Question 9

What is the Henderson-Hasselbalch equation?

Answer 9

pH = pK + log ([HCO3-]/(pCO2x0.23))

where pK = 6.1 and 0.23 is the solubility factor

Question 10

What determines the pH of the blood?

Answer 10

Ratio of [HCO3-] and pCO2

Question 11

The reaction between carbon dioxide and water in RBCs is sped up by which enzyme?

Answer 11

Carbon anhydrase

Question 12

How does bicarbonate exit red blood cells?

Answer 12

Via the chloride bicarbonate exchanger

Question 13

What is responsible for creating the plasma bicarbonate concentration of 25mmol.l-1?

Answer 13

The reaction between carbon dioxide in water that takes place in red blood cells to yield bicarbonate and H+

H+ bind with negatively charged Hb and bicarbonate leaves RBCs via the chloride bicarbonate exchanger

Question 14

What happens to the H+ produced from the reaction between carbon dioxide and water in RBCs?

Answer 14

It binds to negatively charged haemoglobin

Question 15

What does the amount of HCO3- that erythrocytes produce depend on?

Answer 15

Binding of H+ to haemoglobin

Question 16

What is arterial pCO2 determined by?

Answer 16

Alveolar pCO2

Question 17

Is pCO2 higher or lower in venous blood?

Answer 17

Higher - comes from metabolically active tissues

Question 18

If more oxygen binds to haemoglobin and it is in the R state, do more or less H+ ions bind?

Answer 18

Less H+ ions bind - as at lungs

Question 19

If less oxygen binds to haemoglobin and it is in the T state, do more or less H+ ions bind?

Answer 19

More H+ ions bind - as at tissues

Question 20

Describe the binding of Hb at tissues

Answer 20

Less O2 binds -> T state
More H+ ions bind

THEREFORE if Hb binds more H+ in RBCs then more HCO3- can be produced

Question 21

In what 3 forms is CO2 transported?

Answer 21

1) As dissolved CO2 (10%)
2) As hydrogen carbonate (60%)
3) As carbamino compounds (10%)

Question 22

Roughly what is the ratio between CO2 and HCO3?

Answer 22

1:20

Question 23

Why does haemoglobin bind with H+ in the RBC?

Answer 23

To prevent it entering the blood and lowering pH